The present invention relates generally to a driver assistance system for facilitating steering of a vehicle by tracking a target line of a roadway, and more particularly to a lane-following system based on detection of lane markings (usually painted white or yellow lines) on the surface of a roadway.
A number of technologies for lateral control by detection of lane markings have emerged. Some of such technologies are disclosed in U.S. Pat. Nos. 5,913,375, 5,765,116 and 5,979,581. In U.S. Pat. No. 5,913,375, a CCD camera mounted on a vehicle detects the presence of lane markings on a roadway and carries out a lateral control of a vehicle in relation to the detected lane marking. In U.S. Pat. No. 5,765,116, a video camera or a CCD camera is used to detect the presence of lane marking. An associated signal processor estimates the vehicle lateral position in relation to the detected lane markings. An electric motor coupled to the steering mechanism is used to provide a torque input to the steering. A controller is designed to assist the driver to maintain the vehicle lane position using a torque input to the steering. In U.S. Pat. No. 5,979,581, a laser sensor is used to detect three points on a painted lane marking on the surface of a roadway and three points are used to estimate the position of the lane centerline relative to the vehicle, as well as the geometry of the roadway. These technologies rely on detection of lane marking so that lateral control is cancelled or disabled in the absence of detection of lane markings and resumed in the presence of detection of lane markings. If the system is switched on and off frequently, the driver may feel unpleasant and unnecessary stress might be applied to the system. Therefore, there is a need for a new approach to the lateral control of vehicles by detection of lane markings at a preview distance in front of a moving vehicle, which does not induce unnecessary switching on and off the system. The present invention satisfies the need.
An object of the present invention is to provide a lane-following system of facilitating steering of a vehicle by tracking a lane of a roadway, which system is free from undesired switching on and off due to absence of and presence of detection of lane marking.
Another object of the present invention is to provide a method of facilitating steering of a vehicle by tracking a target line of a roadway, which method is free from undesired switching on and off due to absence of and presence of detection of lane marking.
According to one aspect of the present invention, there is provided a lane-following system of facilitating steering of a vehicle by tracking a lane of a roadway, the vehicle having a steering system, said lane-following system comprising:
a look-ahead sensor detecting the presence of lane marking on the surface of a roadway in relation to the vehicle;
a processor estimating the position of the vehicle in relation to said detected lane marking; and
a steering controller rendered operable in the presence of detected lane marking but inoperable in the absence of detected lane marking,
said steering controller, when rendered operable, producing, based on said estimated position of the vehicle, a steering control signal of magnitude to produce, in turn, a bias to the steering system,
said steering controller being operable to determine whether or not said look-ahead sensor has detected the presence of lane marking, and to evaluate the manner in which said look-ahead sensor has failed to detect the presence of lane marking to provide an evaluation result,
said steering controller being held inoperable in response to said evaluation result for a predetermined period of delay time since said look-ahead sensor has resumed to detect the presence of lane marking until said steering controller is subsequently rendered operable upon expiration of said predetermined period of delay time.
According to another aspect of the present invention, there is provided a method of facilitating steering of a vehicle by tracking a target line of a roadway, the vehicle being provided with a steering system, the target line being a line between lane markings defining the lane, comprising:
applying a steering bias to the steering system in such a manner as to assist driver in tracking the target line in the presence of detection of the presence of lane marking;
disabling application of the steering bias to the steering system in the absence of detection of the presence of lane marking; and
resuming application of the steering bias to the steering system upon expiration of a predetermined period of delay time since a change from the absence of detection of lane marking to the presence of detection of lane marking after a predetermined phenomenon had occurred.